Method for shifting multi-speed axles

ABSTRACT

In a shifting mechanism housed in a case a first relatively rotating member rotates about an axis. A second relatively rotating member is selectively coupled and decoupled with the first member. A selector is moveable for actuating the coupling to mutually connect and disconnect the members. A resilient connection is provided between the coupling and selector. A method for shifting multi-speed axles without significant driver interaction by automatic synchronization is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 09/307, 034,filed on May 7, 1999, now U.S. Pat. No. 6,193,629, which is assigned tothe Assignee of the present application and hereby incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of power transmission in adriveline for an automotive vehicle. More particularly, it pertains to amethod of shifting multi-speed axles to drivably connect relativelyrotating shafts in the driveline of a motor vehicle.

2. Description of the Prior Art

To drivably connect relatively rotating shafts, a mechanicalsynchronizer is commonly provided to synchronize the rotational speed ofthe shafts, an example of which is provided in U.S. Pat. No. 4,375,172.The device of the '072 patent is a relatively effective mechanism, butis produced at high cost and not able to engage over a wide speedvariation.

It would be desirable to provide a non-blocked engagement device forengaging relatively rotating shafts.

Also, multi-speed axles are commonly used on vehicle drivelines toincorporate different final drive ratios. This allows, for example, ahighway gear, for fuel economy, and a towing gear, for maximum vehiclepulling power. Multi-speed axles are typically manually operated and arefound on heavy trucks, which have manual transmissions. The use of amanually operated multi-speed axle generally requires a relativelyskilled driver with the ability to properly manipulate the acceleratorpedal during shifts to synchronize engine speed to axle speed, which hasa direct impact on shift smoothness and axle durability.

Currently, the disadvantages of using multi-speed axles, i.e. skilleddrivers and manual transmissions, outweigh the advantages, i.e. improvedfuel economy with maximum pulling power. With the increased consumer useof light trucks and sport utility vehicles, however, improved fueleconomy combined with maximum pulling power and the use of an automatictransmission are very desirable. The need, therefore, is to develop amulti-speed axle capable of providing improved fuel economy and maximumpulling power for use by a typical driver with an automatictransmission.

SUMMARY OF THE INVENTION

To avoid the difficulties and high cost associated with developing andmanufacturing transmissions having a large number of forward speedratios, and in order to improve the cost and performance of shifting ofmulti-speed axles, improved shaft mechanisms and methods for shiftingmulti-speed axles are provided.

In a shifting mechanism housed in a case a first relatively rotatingmember rotates about an axis. A second relatively rotating member isselectively coupled and decoupled with the first member. The couplinghas a first spline tooth with a first axial length longer than the firstspline tooth. The second spline tooth has an end having a frusto-conicalshape. One of the first and second members has a plurality of thirdspline teeth for engagement with the spline teeth of the coupling. Thethird spline teeth have a complimentary frusto-conical shape. A selectoris moveable for actuating the coupling to mutually connect thedisconnect the members. A resilient connection is provided between thecoupling and selector.

Such a shift device allows for shifting on-the-go despite the input andoutput shafts lacking fully synchronized rotational speeds. Such a shiftdevice is useful in many devices, including two-speed axles,subtransmissions (such as secondary transmissions or two-speedgearboxes), 4WD shift mechanism and power take-off units. The shiftmechanism may be coordinated with a computer to synchronize the inputand output speeds to improve the shift “feel” and durability.

Such a mechanism is further improved using an electronic controller toadjust the input and output rotational speeds closer to synchronous,utilizing engine, transmission and ABS control features in conjunctionwith adaptive shift motor controls. Mechanisms and methods for shiftingmulti-speed axles according to the present invention thereaftercompletes the shift at substantially synchronous speeds preferably usinga “snap-action” shift device with minimal driver intervention.

A preferred method of shifting a multi-speed axle in a vehicle inaccordance with the present invention includes requesting a gear ratiochange, synchronizing the speed of the input shaft to the axle with thespeed of the output shaft, and then shifting the axle. The request canbe made manually by the operator or automatically by the enginecontroller based upon vehicle load.

Additional advantages and features of the invention will become apparentfrom the description that follows, and may be realized by means of theinstrumentalities and combinations particularly pointed out in theappended claims, taken in conjunction with the accompanying drawings.

In order that the invention may be well understood, there will now bedescribed some embodiments thereof, given by way of example referencebeing made to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a powertrain for a motor vehicle thatincludes a multiple-speed rear axle assembly utilizing an illustrativeshift device according to the present invention.

FIG. 2 is a representation of a cross-section taken at plane 2—2 of FIG.1.

FIG. 3 is an enlarged view of a portion of the mechanism shown in FIG.2.

FIG. 4 is a partial sectional view of the coupling shown in FIG. 2.

FIG. 5 is an end view of the coupling shown in FIG. 4.

FIG. 6 is a partial side view of the spline teeth of the coupling shownin FIG. 4.

FIG. 7A illustrates a secondary transmission using a shift deviceaccording to the present invention in a first position rotatably lockingthe sun and carrier in a direct drive ratio.

FIG. 7B illustrates the secondary transmission of FIG. 7A in a secondposition to engage a gear reduction.

FIG. 7C illustrates a secondary transmission using an alternative shiftdevice according to the present invention in a first position rotatablylocking the sun and carrier in a direct drive ratio.

FIG. 7D illustrates the secondary transmission of FIG. 7C in a secondposition to engage a gear reduction.

FIG. 7E is a schematic illustration of a vehicle using a secondarytransmission, for example according to FIGS. 7A-7D.

FIG. 8 illustrates a transfer case using a shift mechanism according tothe present invention.

FIG. 9 illustrates a flow chart for a method of controlling amulti-speed axle according to the present invention.

FIG. 9A illustrates a flow chart for a method of shifting a multi-speedaxle according to the present invention.

FIGS. 10A and 10B illustrate a partial sectional side view and end view,respectively, of a secondary transmission using a further alternativeshift device according to the present invention.

FIGS. 11A and 11B illustrate a partial sectional side view and end view,respectively, of a secondary transmission using a further alternativeshift device according to the present invention.

FIGS. 12A and 12B illustrate a partial sectional side view and end view,respectively, of a secondary transmission using a further alternativeshift device according to the present invention.

FIG. 12C illustrates an eccentric cam for the device illustrated inFIGS. 12A-B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described in co-pending U.S. patent application, Ser. No. 08/854,256(the “'256 application”), co-pending U.S. patent application Ser. No.09/307,035, and co-pending U.S. patent application, Ser. No. 09/307,034,having the same inventorship, which are incorporated herein by referencein their entirety, as shown in FIG. 1, the powertrain for a rear wheeldrive motor vehicle includes an engine 10; transmission 12; rear driveshaft 14; rear axle differential 18, left-hand and right-hand rear axleshafts 20, 22; and rear drive wheels 24, 26. The right-hand andleft-hand front drive wheels 28, 30 are not driven in the rear wheeldrive applications, as is known to one skilled in the art. The engine 10is drivably connected to the multiple-speed transmission 12 which isdrivably connected to the drive shaft 14, which is connected to theinput shaft of a multi-speed axle mechanism 32 located within a case orhousing 34.

As described with reference to FIG. 2 in the '256 application, the driveshaft is connected to a beveled input pinion 36 drivably connected to aring gear 38 of a two-speed axle 32 located within housing 34. The ringgear 38 is rotatably supported by the housing 34 at bearings 40, 42. Thering gear 38 is in continual meshing engagement with a plurality ofplanetary pinion gears 44 supported for rotation by pinion carrier 46.The carrier 46 is in continual driving engagement with an interwheeldifferential, and example of which is disclosed in U.S. Pat. No.5,316,106. The differential 18 drives the rear drive wheels 24, 26 aboutan axis of rotation 48 via wheels 24, 26 in a manner known to oneskilled in the art.

As best shown in FIGS. 2 and 3, a coupling 50 is provided in the axlemechanism 32 to mutually drivably connect and disconnect the pinions 44and the carrier 46. The coupling 50 comprises an annular sleeve membercoaxial with the axis 48. The coupling 50 carries a sun gear 52 inmeshing engagement with pinion gears 44. The coupling 50 also carries asecond gear 54 axially displaced from the sun gear 52. The coupling 50is shown in a first position at the right hand side of axis 48, whereinthe coupling 50 provides an underdrive condition by locking pinion gears44 against rotation with respect to housing 34 when coupling 50 engageshousing 34 at the second gear 54. Furthermore, although the presentapplication is described above with reference to an underdrive ratioacross the planetary gearset, in a preferred embodiment, the input gearratio (for example the beveled pinion ratio) is adjusted so theso-called “underdrive ratio” comprises the equivalent of a direct driveratio and the socalled “direct drive” ratio comprises an overdriveratio.

In FIG. 2, the coupling 50 is shown at a second position at the bottomof the axis 48. At this second position, the coupling 50 is axiallymoved to a second position wherein gear 54 is moved out of engagementwith the housing 34. In this second position, the sun gear 52 remains inmeshing engagement with pinion gears 44 while sun gear 52 also engagesthe carrier 46 to mutually rotate the carrier 46 and pinions gears 44 toproduce a direct drive ratio. The coupling 50 is disconnected from thehousing 34 prior to the sun gear 52 being drivably connected to thecarrier 46, otherwise the entire planetary gearset would lock up againstrotation.

As further shown in FIG. 2, sun gear 52 is carried by the coupling 50and is drivably engaged with pinion gears 44 in the underdrive anddirect drive positions. A motor 60 is supported by the housing 34. Themotor 60 moves a shift fork 62 axially to move coupling 50 to a desiredposition to obtain the proper axle ratio. A preferred embodiment of themotor 60 comprises a rotary electric motor, coaxially rotatablyconnected to a shift cam 63 through an approximately 58:1 reduction wormgear. Because of the large gearing reduction through the worm gear, onlya small electric motor is required. The shift cam 63 includes a spiralgroove 67 engaged with the shift fork 62. Thus, as the motor 60 rotatesthe shift cam 63, the spiral groove 67 urges the shift fork 62 axially.The shift fork 62 is supported on a rod 69 which is supported by thehousing 34 for axial movement. Alternatively, one skilled in the artrecognizes the motor 60 may comprise a linear electric motor or a vacuummotor or any equivalent motor for imparting such linear travel in theshift fork. Alternatively, a mechanical connection may impart the axialmovement of the shift fork 62, such as through a Bowden cable connectionas is known to one skilled in the art.

The shift cam 63 preferably includes a detent (not shown), preferablycomprising a detent position (not shown) in the spiral groove 67. Thisdetent is positioned to correspond with the sleeve 50 in a“synchronizing” position as described below. The spiral of the groove 67extends helically around the cam 63, so as the cam 63 is rotated by themotor 60, the shift fork 62 is moved axially approximately 4.5 mm past acentered position, which corresponds to “neutral”. The centered“Neutral” position is where the second gear 54 is not rotatably engagedwith the housing 54 and the sun 52 is not engaged with the carrier 46.Preferably as illustrated in FIG. 3, the second gear 54 is nearlyimmediately adjacent the housing 34 at the neutral position, while thesun 52 is approximately 2.0 mm from engagement with the carrier 46.

The coupling 50 preferably moves axially 9 mm in either direction fromthe centered neutral position, but begins synchronizing with the housing34 of carrier 46 when the shift fork 62 is moved approximately 4.5 mmaxially on either side of the centered neutral, the 4.5 mm positionbeing the “synchronizing” position (alternatively called “neutralplus”). At this “synchronizing” position, within the groove 67, the campreferably has the detent, comprising a portion of the groove 67,extending circumferentially perpendicular to the axis of rotation of thecam 63 (versus helically), so the shift fork 62 is momentarily not urgedfurther axially by the fork while the shift cam 63 continues to rotate.

As shown in FIG. 3, during synchronization, the ball lock mechanism 68disengages the groove 70 of the sleeve, so the sleeve 50 does not moveaxially the entire 4.5 mm. While the shift fork 62 is within the detent,the spline teeth of the sleeve 50 are synchronized as described abovewhile the axial spring provides an axial force on the sleeve 50 to urgethe sleeve into engagement. As the second gear 54 synchronizes with thehousing 34, the spring 66 urges the sleeve rightwardly and the ball lock68 will again engage the groove 70. Once the cam 63 is rotated past thedetent, the groove 67 extends further helically, so that the sleeve 50is urged axially to fully engage the spline teeth as described above foranother approximately 4.5 mm axially. Thus, in this preferredembodiment, the spline teeth are engaged approximately 7-9 mm; howeverone skilled in the art recognizes these distances are applicationspecific and will vary based on the torque being transmitted, as well asthe physical characteristics of the splines and gears.

One skilled in the art recognizes that the detent could alternativelycomprise rotationally stopping the motor 60 at the point where the shiftfork 62 is moved axially within groove 67 approximately 4.5 mm, so thesynchronization can occur when synchronous speeds are obtained andinitial engagement of the spline teeth occur as described above. Speed(RPM) sensors (not shown) preferably detect synchronization, i.e. whenthe spline teeth are initially engaged, and the motor 60 is startedagain to rotate until the spline teeth fully engaged.

A resilient connection 56, described in further detail below, isprovided between the shift fork 62 and the coupling 50 to ensure properforce is applied during engagement of the various members 52, 44, 46,54, 34 to enable proper synchronization and smooth engagement thereof.This arrangement further provides a “snap-action” engagement of theteeth when the rotational speeds are synchronized. This device furtherprovides shock absorption when the members engage. The resilientconnection 56 enables the motor 60 to move the shift fork 62 to anabsolute axial position, while the coupling 50 may not necessarily befully engaged and therefore not properly axially aligned with the shiftfork 62.

One skilled in the art recognizes that an equivalent resilientconnection 56 may be provided between the motor 60 and shift fork 62, orany location between the input to move the shift collar and the shaftsupporting the member to be engaged (i.e. the gear itself could beaxially spring loaded). An example of another preferred resilientconnection between the motor and shift fork is shown in U.S. Pat. No.4,498,350 at 20, 20′, which is incorporated herein by reference for therelevant teachings provided therein.

As shown in FIG. 3, a preferred resilient connection 56 comprises a pairof pre-loaded axial compression springs 64, 66 provided between theshift fork 62 and the coupling 50. The springs 64, 66 are axiallyopposed, each applying an axial force on the coupling 50 when the shiftfork 62 is moved in the direction of the particular spring 64, 66. Thusas shown in FIG. 3, the shift fork 62 is moved rightwardly and spring 66is compressed, thereby imparting an additional axial force on coupling50 through gear 54 until the gears are engaged and the shift fork 62 andcoupling 50 are aligned. The springs 64, 66 are selected to provide aproper force on the coupling 50 to ensure proper synchronization andfull engagement. The springs bias the coupling in the desired direction,and when synchronous speeds are realized due to the teeth, then thecoupling engages rapidly with a “snap action engagement”, where thespring urges the coupling into the final position and the ball lock isreengaged. Further, the springs absorb energy during the initialengagement of the teeth—so as the longer teeth initially engage, thecoupling will move axially against the spring force until rotationalspeeds are synchronous, allowing the coupling to move axially in thedesired direction. The springs thus apply an axial force on the coupling50. Once the spline teeth described below are aligned on the various 52,44, 46, 54, 34 to be engaged, the spring force urges the coupling tosnap into engagement with the member. Likewise, when the shift fork 62is moved leftwardly, the second spring 64 imparts a leftward force uponcoupling 50 through a stop 72 provided on the coupling 50 to provideproper synchronization and engagement force as described above.

Preferably, the resilient connection 56 further includes a ball lockmechanism 68 provided on the shift fork 62. The ball lock mechanism 68is radially displaceable from engagement in a groove 70 provided oncoupling 50. Thus, when the motor 60 rotates and moves the shift fork 62axially, which then urges the coupling 50 rightwardly to engage the gear54 with the housing 34, if the spline teeth on gear 54 and housing 34are not synchronized, the spline teeth axially oppose each other at theconical portion of the spline teeth described below with reference toFIG. 4. Because the motor 60 forces the shift fork 62 rightwardly beyondthe centered “neutral” position before the rotational speeds aresynchronized, the unsynchronized opposing spline teeth resist axialmovement of the coupling 50. This resistance causes the ball lock 68 tocome out of engagement from the groove 70, but the axial spring 66continues to impart an axial force upon the coupling 50 to engage thesecond gear 54 with housing 34. Once the rotational speeds aresynchronized, the spline teeth on the gear 54 engages the housing 34 andthe axial spring 66 causes the coupling 50 to move rightwardly intoengagement with the housing 34 and the ball lock mechanism 68 is alignedwith the groove 70 and is engaged therein. Likewise, when the sun gear52 engages the carrier 46, the shift fork 62 is moved leftwardly. Theball lock mechanism 68 disengages the groove 70 leftwardly and thesecond spring 64 urges the coupling 50 leftwardly until the coupling 50is synchronized with the carrier 46 and engaged therewith, allowing thecoupling 50 to align the groove 70 with the ball lock mechanism 68 ofthe shift fork 62.

As shown in FIG. 3, the coupling 50 is illustrated in a position wherethe motor 60 has moved the shift fork 62 rightwardly and disengaged theball lock mechanism 68. Because the second gear 54 is not synchronizedwith the housing 34, the second gear 54 occupies the leftward positionabutting the housing 34 as shown in FIG. 3. As the second gear 54synchronizes rotation with the housing 34, the second gear 54 movesrightwardly as illustrated in phantom. During this rightward movement,the sun gear 52 also moves rightwardly, away from the carrier 46. Asshown the FIG. 3, during synchronization of the coupling 50 with thehousing 34, the sun gear 52 occupies the center position shown in theright hand portion of FIG. 3. In this position, sun gear 52 is spacedaxially approximately 2 mm from the carrier 46, and is therefore notengaged with carrier 46 and the drive is in a “neutral” state. As thecoupling 50 moves rightwardly into the underdrive position as describedabove, or leftwardly, into the direct drive position as described above,the sun occupies the respective position as shown in phantom.

The engagement of the members 52, 44, 46, 54, 34 is provided through aplurality of circumferentially spaced spline teeth. As shown in FIG. 4,the sun gear 52 is preferably formed integrally on the sleeve 50. Asshown in end view FIG. 5, the sun gear 52 comprises a plurality ofcircumferentially spaced spline teeth 51, 53. The sun gear 52 teeth 51,53 have flat contact surfaces for engagement with complimentary teethprovided on the planetary pinion gears 44 and the carrier 46. As isknown to one skilled in the art, the flat contact surfaces of the teeth51, 53 may include small spiral shaped grooves (not shown) for carryinglubrication.

In a preferred embodiment, the teeth are synchronized mechanically. Asshown in FIG. 6, every other tooth 51 is preferably recessed axiallyfrom adjacent teeth 53, so lockup is more easily obtained atsynchronizing speeds. If the rotational speeds are synchronizedelectronically as explained below, the recessed teeth are lessnecessary. As is shown in FIG. 4, the teeth of sun gear 52 include acone angle 57 optimized for synchronization with a complimentary coneangle provided on the teeth of the carrier 46. The teeth of the sun gear52 preferably further include a tapered surface 59 at the leading edgeof the teeth 51, 53 to facilitate engagement of the sun gear 52 andcarrier 46. The spline tooth spacing is optimized to minimize backlash.The second pair of teeth 54 on the coupling 50 are similarly formed tosynchronize the rotational speed of the coupling 50 when engaging theteeth on the housing 34

In another preferred embodiment, the rotational speeds of the members52, 44, 46, 54, 34 are synchronized electronically using the enginecontroller and/or the anti-lock braking system of the motor vehicle. Asshown in FIG. 1, sensors 73, 74 are provided to measure the rotationalspeed of the input and output of the differential 18. The input speed ispreferably measured by obtaining the output speed of the transmission 12using sensors 73, 74 as is known in the art. As shown in FIG. 2, basedon the reduction of the input pinion 36, the rotational speed of thering gear 38 is known. The rotational speed of the planetary piniongears 44, sun gear 52, and carrier 46 is calculated based on theposition of the coupling which mutually connects and disconnects severalof the members 52, 44, 46, 54, 34 as described above.

The output speed of the differential 18 is preferably inferred bymeasuring the rotational speed of the wheel 24 using an anti-lockbraking system (ABS), which is known to one skilled in the art and notdescribed here in detail. In a preferred embodiment, the ABS systemincludes an ABS sensor illustrated as sensor 74, such an ABS sensorbeing known to one skilled in the art. The speed of the wheel 24 may beused to estimate the rotational speed of the carrier 46 whendifferential action is not occurring. Thus, to electronically controlthe synchronization of the members 52, 44, 46, 54, 34, the input speedof the input gear 36 or output speed of the differential 18 may becontrolled. As will be appreciated by the description provided herein,the sensors 73, 74 may be located in various positions to provide thesignal indicating the input and output rotational speeds.

Preferably, the sensors 73, 74 send a signal to a computer 76, such asan engine control unit (ECU). The computer 76 then determines whether itis proper to have the axle in an underdrive or direct drive positionbased on the rotational speeds of the driveline. Once this determinationis made, the computer 76 provides a signal to control the rotationalspeeds of the input or output shaft to synchronize the rotation of themembers 52, 44, 46, 54, 34 by controlling the engine speed, anti-lockbrakes or transmission. The speeds are thus synchronized by using theECU to increase or decrease the rotational speed of the engine 10 ortransmission 12 in a manner known to one skilled in the art, or bydecreasing the output rotational speed of the differential 18 by usingthe anti-lock brake system (ABS) to apply a brake at one or more of therear wheels 48, 26 as is also known to one skilled in the art. As therotational speeds are thus synchronized, the motor 60 is commanded bythe computer 76 to move the shift fork 62 to the desired position tocreate the proper ratio.

In a preferred embodiment, a further sensor 75 is provided to sense theposition of the shift fork 62 and to determine if the shift fork is inthe proper position and preferably within the proper “synchronizationtiming window” to engage smoothly and to obtain the desired ratio. This“timing window” is provided in the period at which the rotational speedsare substantially synchronous. In FIG. 2, the sensor 75 is illustratedschematically as an encoder provided on the motor 60, but could beincorporated in the case to sense the fork or coupling, or any otherpart of the mechanism. The rotational speed sensors 73, 74 then measurethe rotational speeds and the computer 76 calculates whether the properratio is actually engaged. Such a sensor 75 may be of any known form,such as an encoder, a linear position sensor, a Hall Effect sensor, alimit switch, or any other known positional sensing devices.

The positional signal provided by the sensor 75 is preferably furtherused to enable the controller to adjust the axial shifting speedprovided by the motor 60 and thereby position the mechanism in theproper axial position when the rotational speeds are synchronized—i.e.the shaft speeds are synchronized within a short “time window” throughwhich the device preferably axially moves the shift fork to soften theshift harshness; the motor 60 is controlled to shift through this “timewindow” at which the rotational speeds are substantially synchronous.

Selection of the underdrive ratio may be performed automatically by thecomputer 76 commanding a shift when appropriate as described above.Otherwise, such a shift may be commanded manually by the operator movinga lever or a switch 78 to a desired position, such as commanding anunderdrive position. Preferably the switch 78 includes a digital displayto indicate the presently engaged ratio or mode (such as underdrive orperformance). For example, a light may be illuminated when underdrive isengaged. Alternatively, an indicator may be provided on the instrumentpanel cluster to indicate the ratio.

An axle according to the present invention may thus be used to multiplythe number of gear ratios in an existing transmission. In such anarrangement, a shift of the axle may be commanded simultaneously duringa shift of a gear in the transmission to multiply the transmission ratioacross the axle to obtain a wider range transmission. For example, thirdgear may be reduced using the axle to produce a final drive ratiobetween first and second gears in the transmission. In such an example,movement of a manual shift lever to what was previously second gearposition would cause third gear to be engaged and the axlesimultaneously shifted to underdrive. Upon movement of the shift leverto what was previously third gear, the second gear would be engaged andthe axle simultaneously shifted to the direct drive position.

Although described herewith reference to a differential on a rear wheeldrive vehicle, the present concepts may readily be applied by oneskilled in the art to another drive configuration. For example, thepresent invention may be added before or after the transmission ineither a front wheel drive or rear wheel drive vehicle to provideadditional gear reduction or increase the number of gear ratios providedthereby. An example of such an application in a front wheel driveapplication is described in U.S. Pat. No. 5,474,503, assigned to theassignee of the present invention, which is incorporated herein byreference. In such an instance, the input to the planetary gearsetcomprises a direct rotational input instead of a beveled pinion gear asillustrated in FIG. 1. In this case, the secondary transmission (ortwo-speed gearbox) provides an additional reduction to increase thenumber of gear ratios available. A clutch according to the presentinvention may be provided in a device according to the '503 patent toengage the ring with the one way clutch, or such a device may be used inplace of the transfer clutch. As would be appreciated by one skilled inthe art, the present invention is capable of doubling the number of gearratios produced by such a transmission. For example, a four speedtransmission may be used in an application to provide up to eightforward speed ratios using a secondary transmission or an axle accordingto the present invention.

A rear wheel drive secondary transmission (alternatively called asubtransmission or two-speed gearbox) is illustrated in FIGS. 7A-D.FIGS. 7A and 7B illustrate a first embodiment, while 7C-7D illustrate asecond embodiment. The reference numbers remain the same in each 7A-7Dexcept where the design differs.

In a secondary transmission according to the present invention, a shiftmechanism 710 is provided to shift a secondary transmission 712 for arear wheel drive vehicle. The secondary transmission 712 is locatedbehind the primary transmission 12 illustrated in FIG. 1. Preferably,the transmission 12 includes a flange at the rear end thereof and thesecondary transmission 712 may be selectively mounted at 713 thereto onan optional basis to provide additional gear ranges, or an optionaloverdrive system The shift device 710 is similar in many manners to thedevice previously described in FIGS. 2-6, but the shift fork of thatdevice is replaced by a lever attached to a ball screw drive 716. Asmotor 720 rotates, ball screw drive 716 is forced axially. Thistranslates the end of lever 714 attached thereto.

The lever 714 rotates about a pivot 718 to translate the opposite end ofthe lever 714 a proportional distance (of course the lever 714 travelsin an arc, the linear vector is presently of interest) The lever 714includes a bifurcated end 722 (for the sake of clarity, one end is shownin phantom in this partial sectional view) which engages an annulargroove 724 provided in a sleeve 726 engaged with a coupling 750.Preferably the motor 720 includes a known encoder 721, illustratedschematically, for determining the rotational position thereof. Thecontroller preferably interprets a signal from the encoder 721, andafter interpreting the position of the motor 720, the controllercommands the motor 720 to shift the coupling within the “time window”during which the input and output speeds are substantially synchronous.

The coupling 750 has a splined connection 727 to the sun gear 752 andone skilled in the art appreciates this device operates in a mannersimilar to that described above with reference to the axle above andtherefore the operation will not be described in great detail here. Asshown in FIG. 7B, the coupling 750 is slid from the position shown inFIG. 7A where the sun 752 and carrier 746 were locked to a positionwhere the coupling 750 is moved rightwardly as viewed in FIG. 7B to aposition where the coupling 750 is drivably disengaged from the carrier747. Preferably this produces a reduction to develop an underdrive ratioacross the planetary gearset. One skilled in the art could develop avariety of reductions and rotational reversals in a known manner andtherefore these will not be discussed here in detail.

A compression spring 730 is provided between the sleeve 726 and coupling750 and functions in a manner similar to the springs 64, 66 describedabove with reference to FIGS. 2 and 3, by providing a resilientconnection at either end 732, 734 between the input force provided bythe shift mechanism 710 and the coupling 750. Further, a shift positiondetent, or ball lock mechanism 736, is provided to retain the coupling750 in a manner similar to that described above, thereby retaining thedesired gear engagement. A screw 738 is provided to install the balllock mechanism 736 on the coupling 750, and in one embodiment is used toadjust the force of the ball lock mechanism. As shown in FIG. 7A, theball lock mechanism engages one of a pair of grooves provided in thesleeve 750, each groove corresponding to an “end detent position”, suchthat the ball lock mechanism 736 in this embodiment operates to engage apair of terminal grooves, versus the central groove 70 shown in FIG. 2.The planetary gear engagement, as illustrated in FIGS. 7A-B, includes ahelical engagement between the sun gear 752 (part of the splined 727sleeve 750) and planets 744. As appreciated by one skilled in the art,this design provides axial thrust bearings adjacent the gears 752, 754to accommodate the resultant thrust loads.

FIGS. 7C-7D illustrate a variation to the embodiment shown in FIGS.7A-7B. In this embodiment, the coupling 750′ carries the sun gear 752′and the splined connection 727 of FIGS. 7A and 7B is eliminated. Afeature of this embodiment is that the gear engagement between the sun752′ and planetary gear 744 comprises a simple spur gear profile, thusenabling translation of the coupling 750 directly and minimizing anyaxial loading. One skilled in the art appreciates the straight spur gearengagements, such as the sun 752 to planets 744 in FIG. 7C-7D,contrasted to the embodiment of FIGS. 7A-B, provide for minimal axialgear reactions.

Further alternative shifting devices are provided in FIGS. 10-12. Theseembodiments are similar to the devices described above, in that theyutilizes many of the same components but these embodiments have agenerally more simple shift device. These devices are illustrated in useas a secondary transmission, but one skilled in the art appreciates theapplicability to other devices as described above. In the embodiment ofFIGS. 10A and 10B, an electric motor 720′; is connected through a shaftto a link 714′. The link 714′ is in the form of a shift fork and engagesa slot in the coupling 750″ through a snap-action device 724′. Thesnap-action device 724′ provides a resilient connection between the link714′ and coupling 750″ in a manner similar to the embodiments describedabove and is therefore not described in greater detail here.

In the embodiment of FIGS. 12A, and B, and C, an electric motor 720′; isconnected to a reduction gearbox 716′, which is subsequently connectedto a link 714′. The link 714′ is in the form of a shift fork and engagesa slot in the coupling 750″ through a snap-action device 724′. Anencoder illustrated schematically at 721′, senses the position of thegearbox 716′, or alternatively the motor 720′. The snap-action device724′ provides a resilient connection between the link 714′ and coupling750″ in a manner similar to the embodiments described above and istherefore not described in greater detail here.

In the embodiment of FIGS. 12A, B and C, an electric motor 720′; isconnected to an eccentric pivot 723, which is subsequently connected toa link 714′. The link 714′ is in the form of a shift fork and engages aslot in the coupling 750″ through a snap-action device 724′. Thesnap-action device 724′ provides a resilient connection between the link714′ and coupling 750″ in a manner similar to the embodiments describedabove and is therefore not described in greater detail here. The link714′ rotates about a pivot 725 to effect a translation of the coupling750″. The eccentric device is illustrated in FIG. C from right to leftin an end view of a mid position, then a side view of the same position.As the motor 720′ rotates, the eccentric pivot device 723 rotates in abifurcated end 729 of the link 714′, thereby causing rotation of thelink 714′ about the pivot 725.

Preferably, at the time the shift fork is in its “detented endpositions”, the eccentric cam effect of this embodiment generates theadditional shift force required to overcome the ball lock mechanism 738so the ball is forced out of the detent, thereby reducing the shifttorque requirement for the electric motor 720. Thus, a smaller motor 720may be used and/or the gear reduction 716 (ref. FIG. 11B) may be reducedor eliminated.

Furthermore, the present invention may use an adapter to bolt onto anexisting transmission case and thereby require no additionalmodifications to the transmission, particularly when this device is usedon an optional basis in production.

As illustrated schematically in FIG. 7E in a preferred embodiment, thesecondary transmission 712 of FIGS. 7 through 7D are utilized incombination with an automatic transmission 12′ attached to an engine10′. In this arrangement, the electronic control logic of thetransmission 12′ is preferably adapted to change the gear shift sequenceand clutch slippage in a known manner to further improve thesynchronization of the input and output shaft speeds during a shift ofthe secondary transmission 712, and thereby improve the shift smoothnessof the secondary transmission 712, bringing about the shifts in acoordinated manner. The transmission controls may be used in conjunctionwith the engine and anti-lock brake controls as described above.

As described above, the shifting of the device in FIGS. 7-7D are mostsmoothly accommodated by nearly synchronizing the rotational speeds ofthe input and output prior to engaging the shift mechanism 710. This isbest accomplished by monitoring the input/output speeds using sensors asis known to one skilled in the art, for example using a transmissionsensor 761 and driveshaft sensor 762. Examples of such sensors includeABS sensors, turbine speed sensors, or any other such known sensor usedto measure the rotational speed of the vehicle driveline. A controller763 receives signals from the sensors and adjusts the input/outputspeeds by controlling the rotational speed of the engine 10′ and/or thewheels 24′-30′. Such a controller 763 comprises one or more knowncontrollers, such as an engine controller, an anti-lock brakecontroller, a traction control controller (utilizing ABS and/or enginecontrols), and/or an automatic transmission controller, preferably whilesimultaneously adjusting the shift motor speed by monitoring the shiftmotor position sensor 721′ to allow adequate time for input/output shaftrotational speed changes in order to substantially synchronize thespeeds thereof. Simultaneously, the controller adjusts the shift motorspeed to allow adequate time for input/output shaft speed changes beforethe coupling is urged into position, thereby smoothing the engagementthereof. Of course the device 710 acts to provide the snap-action shiftas described above, so the speeds need not be synchronized forengagement. However, by controlling the motor 720, the engagement istimed to enable smooth shifting.

FIG. 9 is a flow chart for a method of controlling a multi-speed axle 32according to the present invention. Referring to step 772, a request toshift multi-speed axle 32 into direct-drive or under-drive can begenerated one of several ways. One way is by driver activation of aswitch 78 to manually request direct-drive or under-drive for eitherhighway or towing conditions. Another way to request a shift is when theengine controller determines that vehicle loading is higher or lowerthan some configurable predetermined limit, such limit corresponding toa known value indicating that the multi-speed axle 32 should be shifted.In this case, the engine controller would request controller 76 to shiftmulti-speed axle 32 to direct-drive during light loads and under-driveduring heavy loads. One skilled in the art could develop additional waysto generate a request for a shift.

Upon receiving a request to shift, the sequence proceeds to step 774.Vehicle speed is checked in step 774 as to whether the vehicle is lessthan a configurable predetermined value corresponding to a value fromwhich it will be known that it is acceptable to shift multi-speed axle32. If the vehicle speed is less than this configurable predeterminedamount, then the multi-speed axle 32 can be shifted and the sequenceproceeds to step 778. In the preferred embodiment, vehicle speed isfirst checked to determine whether the vehicle is stationary. If thevehicle is stationary, then the multi-speed axle 32 can be shifted andthe sequence proceeds to step 778.

Referring back to step 774, if the vehicle speed is less than aconfigurable predetermined value, then the sequence proceeds to step778. In preparation for shifting multi-speed axle 32, the enginecontroller reduces engine torque sufficiently to ease shiftingmulti-speed axle 32 in step 778. After engine torque is reduced, thesequence proceeds to step 780.

Referring back to step 778, after engine torque is reduced, then thesequence proceeds to step 780 where multi-speed axle 32 is shifted intoa neutral position to allow the input shaft 14 and the output shaft 20to be synchronized. After the multi-speed axle 32 is shifted intoneutral, the sequence proceeds to step 782.

Referring back to step 780, after multi-speed axle 32 is shifted intoneutral, the sequence proceeds to step 782 where input 14 and outputshafts 20, 22 are synchronized. Input 14 and output shaft 20synchronization is desirable to provide smooth multi-speed axle shiftingand improve durability. There are several ways in which the input andoutput shafts can be synchronized. One way involves controlling enginetorque while monitoring input and output shaft speed. Engine torque canbe increased or decreased to increase or decrease input shaft speed tomatch the speed necessary to synchronize with output shaft speed.Another method involves using the anti-lock braking system to decreaseoutput shaft speed to match the speed necessary to synchronize withinput shaft speed. A third alternative could involve using a combinationof engine torque and braking manipulation to synchronize input andoutput shafts. One skilled in the art could develop additional efficientmethods for synchronizing input and output shaft speeds. Once the inputand output shaft speeds are synchronized to within a configurablepredetermined amount corresponding to an amount from which it is knownthat an acceptable shift can occur, then the sequence proceeds to step784.

Referring back to step 782, after input 14 and output shafts 20, 22 aresynchronized, then the sequence proceeds to step 784 where multi-speedaxle 32 is shifted to direct-drive or under-drive before engine torqueis restored. After the multi-speed axle 32 is shifted, then the sequenceproceeds to step 788 where the engine controller restores engine torqueand normal driving resumes.

Referring back to step 774, if the vehicle speed is greater than aconfigurable predetermined value, then the sequence proceeds to step776. Engine RPM is checked in step 776 as to whether the engine RPM iswithin a configurable predetermined range corresponding to a range fromwhich it will be known that multi-speed axle shifting can occur. If theengine RPM range exceeds this configurable predetermined range, then thesequence returns to step 774. If the engine RPM range falls within theconfigurable predetermined range,

FIG. 9A illustrates a portion of the controller flow chart for a methodof shifting a multi-speed axle 32 according to the present invention.Specifically, flow chart 9A describes steps 782 and 784 of FIG. 9, andthus controlling the multi-speed axle 32 in more detail. Referring backto step 780 (FIG. 9), while the multi-speed axle 32 is being shiftedinto neutral, the sequence proceeds to step 790. Motor position ischecked in step 790 as to whether the motor has driven the multi-speedaxle 32 into a neutral position. If a neutral position has not beenachieved, then the sequence repeats step 790. Once a neutral position isachieved, then the sequence proceeds to step 792.

Referring back to step 790, once multi-speed axle 32 reaches a neutralposition the sequence proceeds to step 792 where the motor 60 is haltedwhile engine speed is calculated to synchronize input and output shaftspeeds.

Referring back to step 792, after the motor is halted, the sequenceproceeds to step 792 where input 14 and output shafts 20, 22 aresynchronized. Engine torque is increased or decreased to increase ordecrease engine speed to match the speed necessary to synchronize withoutput shaft speed. After engine RPM is changed, the input and outputshaft speeds are compared in step 796. If the input and output shaftspeeds are within a configurable predetermined amount corresponding toan amount from which it will be known that an acceptable shift canoccur, then the sequence proceeds to step 797. IF the input and outputshaft speeds exceed a configurable predetermined amount, then thesequence returns to step 794.

Once the input and output shaft speeds are synchronized, the motorshifts multi-speed axle 32 to a direct-drive or under-drive in step 797.While the motor is shifting multi-speed axle 32 to a direct-drive orunder-drive gear, the sequence proceeds to step 798. Motor position ischecked in step 798 as to whether the motor has driven multi-speed axle32 into a direct-drive or under-drive gear position. If a direct-driveor under-drive gear position has not been achieved, then the sequencerepeats step 794. Once a direct-drive or under-drive gear position isachieved then the sequence proceeds to step 799 where the motor ishalted and the sequence proceeds to step 788 (FIG. 9).

As illustrated in FIG. 8, a shift device 810 according to the presentinvention may be applied in an application including a four wheel drivetransfer gearbox. The planetary gearset 812 would provide a gearingreduction in a transfer gearbox to provide a reduction from a four wheelhigh ratio to a four wheel low ratio in a manner known to one skilled inthe art. Such a device is described in U.S. Pat. No. 4,718,303, which isincorporated herein by reference. However, the coupling mechanism,embodied as clutch plates in the '303 patent, are replaced by the shiftmechanism 810 to replace the clutch plates as the coupling mechanism.

A device according to the present invention enables a shift to produceeither a transfer to 4WD or a 4WD Low reduction to occur while thevehicle is moving, because the synchronization device and techniquestaught herein provide for such reduction in a transfer gearbox in asmooth manner. The function of this device is similar to the otherdevices described above, and is therefore not described in great detail.An electric motor 820 acts through a reduction gearbox 821 having aninternal sensor (not shown) to detect position to move a rotating camdevice 816, similar to that described above. The rotating cam device 816includes a cam follower sleeve provided at the end of the shift fork 862to actuate a shift fork 862 to translate a spring-loaded coupling 850 asdescribed above. The coupling 850 is splined 827 to the output shaft foraxial movement while remaining rotatably engaged thereto.

The coupling 850 engages the planetary carrier 846 for a reductionacross the planetary gearset for 4WD Low range, or alternatively, thesun gear 852 for 4WD high or 2WD ranges (not shown in the alternateposition). One skilled in the art appreciates that this device can beequally applied to a secondary transmission as described above for agear reduction in 2WD mode, or for a 2WD system (versus the 4WD systemillustrated in FIG. 8). A separate device 870 is provided in FIG. 8 toengage the 4WD feature. This device 870 could be a similar snap-lockdevice as described above or a conventional 4WD engagement as known toone skilled in the art.

Although not illustrated, one skilled in the art also appreciates thepresent invention may be used in a layshaft transmission to engage ajournalled gear with a relatively rotating shaft and thereby replace ablocked synchronizer as is typically used.

One skilled in the art will appreciate the disclosed mechanism iscapable of reliably engaging the relatively rotating members atrelatively high differential rotational speeds, but such engagement maybe perceived by the driver or passengers of the motor vehicle as beingtoo harsh. Therefore, a preferred embodiment further includes somesynchronization of rotational speeds prior to engagement. These methods,as described above and appreciated by one skilled in the art, includethe use of engine speed control through the powertrain control module,ABS systems or traction control systems. Using these techniques, one isreadily able to improve the smoothness of engagement, and thereforeimprove the feel of the shift to the passengers of the vehicle.Preferably the shift smoothing capabilities of an automatic transmissioncontroller and mechanisms are also used to synchronize a device andprovide smooth engagement thereof.

The forms of the invention shown and described herein constitute thepreferred embodiments of the invention; they are not intended toillustrate all possible forms thereof. The words used are words ofdescription rather than of limitation, and various changes may be madefrom that which is described here without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method of shifting a multi-speed axle in avehicle, the multi-speed axle having an input shaft, an output shaft,and a gear set having a plurality of members adapted to produce multipledrive connections between the input shaft and output shaft when aselector couples said members between said input shaft and output shaft,said method comprising the steps of: requesting a gear ratio change;determining if the vehicle is stationary; synchronizing a first speed ofsaid input shaft with a second speed of said output shaft; and shiftingsaid multi-speed axle.
 2. A method of shifting a multi-speed axle asrecited in claim 1, further comprising the step of determining if theengine RPM is within an acceptable range.
 3. A method of shifting amulti-speed axle as recited in claim 1, further comprising the step ofsaid engine controller reducing engine torque whereby shifting effort isreduced.
 4. A method of shifting a multi-speed axle as recited in claim1, further comprising the step of shifting to a neutral gear ratio.
 5. Amethod of shifting a multi-speed axle as recited in claim 4, furthercomprising the step of energizing a motor to shift said axle into aneutral gear ratio.
 6. A method of shifting a multi-speed axle asrecited in claim 1, further comprising the steps of: energizing a motorto shift said axle into a neutral gear ratio; and monitoring said motorposition.
 7. A method of shifting a multi-speed axle as recited in claim4, further comprising the step of halting said motor in said neutralgear ratio.
 8. A method of shifting a multi-speed axle as recited inclaim 1, further comprising the step of controlling engine torque tosynchronize a first speed of said input shaft with a second speed ofsaid output shaft.
 9. A method of shifting a multi-speed axle as recitedin claim 8, further comprising the step of monitoring and comparing saidfirst speed and said second speed to generate a speed difference.
 10. Amethod of shifting a multi-speed axle as recited in claim 9, furthercomprising determining if said speed difference is within an acceptablerange.
 11. A method of shifting a multi-speed axle as recited in claim8, further comprising the step of energizing a motor to shift said axleinto said requested gear ratio.
 12. A method of shifting a multi-speedaxle as recited in claim 1, further comprising the steps of: controllingengine torque to synchronize a first speed of said input shaft with asecond speed of said output shaft; energizing a motor to shift said axleinto a neutral gear ratio; and monitoring said motor position.
 13. Amethod of shifting a multi-speed axle as recited in claim 8, furthercomprising the step of halting a motor in said requested gear ratio. 14.A method of shifting a multi-speed axle as recited in claim 1, furthercomprising the step of restoring engine torque.
 15. A method of shiftinga multi-speed axle as recited in claim 1, wherein the step of requestingcomprises a driver activating a switch to request a gear ratio change.16. A method of shifting a multi-speed axle as recited in claim 1,wherein the step of requesting comprises an engine controller thatdetermines a desirable final drive to request a gear ratio change.
 17. Amethod of shifting a multi-speed axle as recited in claim 16, whereinsaid engine controller requests a higher gear ratio upon detecting ahigh vehicle load.
 18. A method of shifting a multi-speed axle asrecited in claim 16, wherein said engine controller requests a lowergear ratio upon detecting a light vehicle load.